The separation of a sour (e.g., sulfur containing) synthesis gas (“syngas”), for example as obtained from the gasification of solid or liquid carbonaceous feedstock, is often used to obtain a H2 product stream suitable for use, for example, in chemical plants, refineries, or as fuel for a gas turbine. It is known that the H2 constituent of NH3 or MeOH syngas can be produced from a variety of processes, such as steam reforming of natural gas or naphtha, partial oxidation of hydrocarbon feedstocks, gasification of solid fuels, or other similar processes. However, such processes could result in a crude syngas stream containing the desired H2, but also containing impurities like CO2, CO, CH4, N2, Ar, H2S, COS, H2O, and others. For example, CO2 might arise from combustion of the feedstock during gasification, the concentration of which is increased if the crude syngas steam is subjected to a water-gas shift reaction to convert by reaction with H2O all or part of the CO in the stream to CO2 and H2. The H2S arises from the reduction of sulfur present in the feedstock during gasification and from further conversion of other sulfur species in the crude syngas stream to H2S during the water-gas shift reaction. Due to concerns over greenhouse gas emissions, there is a desire to remove CO2 from syngas prior to its use (e.g. as a combustion fuel). H2S is also desirably removed from the syngas as it could be a poison for downstream processes, or because if the syngas is combusted in a gas turbine, the H2S is converted into SO2, which has legal limits on its emission in the combustion exhaust gas.
Therefore, the stream is typically purified by additional processing, for example such processes as shift conversion (full/partial) for removal/reduction of CO content in the mixture, acid gas removal (AGR) by absorption, and final purification of gas mixture to increase recovery or control reaction stoichiometry for the final product. Commercial AGR by absorption processes use a liquid solvent (e.g., Selexol™, Rectisol®, etc.) that removes the CO2 and H2S from the syngas. If ammonia is the desired end product, an energy intensive N2 wash operation is employed downstream of the AGR to remove impurities from the H2. Due to ecological and environmental regulation, other operations might be required for converting H2S to elemental sulfur or sulfuric acid and/or for compressing the CO2 for geological storage or enhanced oil recovery (EOR). However, such AGR and additional purification processes are costly (both in terms of capital and operating cost) and require significant power consumption. Thus, there is a need to reduce the overall costs of syngas processing while recovering the highest amount of the desired products as possible.